To debug CoffeeScript, TypeScript, and Dart code,
you need source maps generated in addition to the JavaScript code.
Source maps set correspondence between lines in your original code and in the generated JavaScript code,
otherwise your breakpoints will not be recognised and processed correctly.

JavaScript and source maps are generated by transpiling the original code manually using the File Watcher of the corresponding type
(CoffeeScript, TypeScript, or Dart.
After that you can debug the output JavaScript code.